Assuming you are using a P2T-A11 or A12 from a USDM Civic Si it doesn't have an immobilizer in it. I don't know about the b20 post, there is a lot of back and forth as to if it will work correctly or not on this forum, I will let someone else answer that. If the EX is a manual it should be plug and play, I believe you will need to extend the wiring for vtec and the plugs for the distributor are different (this can be fixed by getting a jumper harness or repining the plug on either the distributor or the engine harness).

If I am wrong on the plug and play part, hopefully someone will correct me. Its been awhile since I have messed with this stuff. lol